1. Field of the Invention
The present invention relates to an axial flow turbomachine rotor of the type comprising a disc having a plurality of flanges extending radially outwards from its periphery in such a manner as to define a plurality of annular grooves between said flanges, a plurality of blades secured to the disc so that they are evenly arranged around the periphery of the disc and extend radially outwards therefrom, each blade having a notched root defining heels which are received in respective ones of the annular grooves of the disc, and a plurality of separate platforms fixed to the disc so that each is disposed between two adjacent blades to define the disc side of the fluid flow path between the blades when the rotor is operating.
2. Summary of the Prior Art
Axial flow turbomachine rotors using blades without integral platforms are known, the blades each having a root which has a comb type attachment which is fixed by an axial pin to the annular flanges of the disc. This type of blade attachment simplifies the manufacture of the disc compared to a disc having non-notched blades requiring axial sockets on the periphery of the disc. The problem posed, however, especially for the large chord blades used in fans and compressors, is the accommodation of stresses in all directions and, in Particular, the accommodation of the tangential components of the forces applied to the blades.
U.S. Pat. No. 3,694,104 describes a blade of composite material in which the root is notched and has heels each having a hole defined by a metal bush or sleeve intended to cooperate with a pin. The root of the blade is fixed to the flanges of the disc by means of two axially offset pins, one being situated on the upstream side of the blade in the leading edge plane, and the other on the downstream side in the trailing edge plane This arrangement does not enable the pins to accommodate the whole of the forces applied to the blades. Thus, the separate platforms interposed between the blades are biased for the accommodation of the tangential components of the forces, and they must be rigid and firmly fixed to the disc by fixing screws, which increases the weight of the rotor. Moreover, the angular offset between the axis of the upstream pin and the axis of the downstream pin creates difficulties in the construction of the blade and of the disc. Some pins and fixing screws are mounted from the front face of the disc, and others from the rear face. This necessitates removal of the rotor if it is to be dismantled.
In other types of rotor constructions, the tangential forces are accommodated by the fixing pin of the blade root thanks to curvilinear surfaces at the end of the root which fit perfectly on the cylindrical surfaces of the disc. U.S. Pat. No. 4,361,416 discloses such an arrangement of the blades, which leads inevitably to an increase of the mass of the blade root.